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Diffstat (limited to 'Documentation/memory-barriers.txt')
| -rw-r--r-- | Documentation/memory-barriers.txt | 19 |
1 files changed, 10 insertions, 9 deletions
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt index 6dafc8085acc..a02d6bbfc9d0 100644 --- a/Documentation/memory-barriers.txt +++ b/Documentation/memory-barriers.txt @@ -1920,9 +1920,6 @@ There are some more advanced barrier functions: /* assign ownership */ desc->status = DEVICE_OWN; - /* force memory to sync before notifying device via MMIO */ - wmb(); - /* notify device of new descriptors */ writel(DESC_NOTIFY, doorbell); } @@ -1930,11 +1927,15 @@ There are some more advanced barrier functions: The dma_rmb() allows us guarantee the device has released ownership before we read the data from the descriptor, and the dma_wmb() allows us to guarantee the data is written to the descriptor before the device - can see it now has ownership. The wmb() is needed to guarantee that the - cache coherent memory writes have completed before attempting a write to - the cache incoherent MMIO region. + can see it now has ownership. Note that, when using writel(), a prior + wmb() is not needed to guarantee that the cache coherent memory writes + have completed before writing to the MMIO region. The cheaper + writel_relaxed() does not provide this guarantee and must not be used + here. - See Documentation/DMA-API.txt for more information on consistent memory. + See the subsection "Kernel I/O barrier effects" for more information on + relaxed I/O accessors and the Documentation/DMA-API.txt file for more + information on consistent memory. MMIO WRITE BARRIER @@ -2903,7 +2904,7 @@ is discarded from the CPU's cache and reloaded. To deal with this, the appropriate part of the kernel must invalidate the overlapping bits of the cache on each CPU. -See Documentation/cachetlb.txt for more information on cache management. +See Documentation/core-api/cachetlb.rst for more information on cache management. CACHE COHERENCY VS MMIO @@ -3083,7 +3084,7 @@ CIRCULAR BUFFERS Memory barriers can be used to implement circular buffering without the need of a lock to serialise the producer with the consumer. See: - Documentation/circular-buffers.txt + Documentation/core-api/circular-buffers.rst for details. |